1. Field of the Invention
The present invention relates in general to closures and more particularly to a return mechanism for automatically returning a closure to a given position. The invention is applicable to closing doors, especially the return of sliding doors to a closed position. The present invention also relates to running gear, including running gear for sliding doors.
2. Related Art
Often a door or other closure may be left open unintentionally after use, such as a refrigerator door, or a door may be left closed unintentionally, such as a door over a ventilator opening. It may be costly or undesirable for many types of closures to remain open after use, and it is, therefore, desirable to provide a mechanism for automatically closing the opened door or opening the closed door. Such closures include sliding doors as in a patio door or a commercial refrigerator door, hatches, stereo cabinets, swing doors, sash windows, or any closure movable from either an open position to a closed position or vice versa.
One type of closure for which a self return mechanism is particularly desirable is a sliding door often used for commercial refrigerators and refrigerated display cases. Commercial refrigerators and refrigerated display cases are employed in markets, food-vending operations and the like for the simultaneous preservation of freshness and attractive display of foodstuffs to the customer. Typically, commercial display cases have surrounding frames around an opening in a display case with tracks for supporting and guiding large sliding doors which incorporate large areas of multiple layered glazing to permit the customer to see, select and access the refrigerated product easily, while preventing what is termed a heat loss into the refrigerated space, namely letting warm air into the refrigerated section.
The customer may view the foodstuff in the refrigerator which they wish to purchase, open the sliding door to the refrigerated area, and remove the foodstuff for purchase. Occasionally, the customer may forget to close the sliding door to the refrigerated area. When the sliding door is left open, large amounts of heat are let into the refrigerated section, possibly leading to the spoilage of the foodstuffs while reducing the efficiency of the refrigerator and wasting valuable energy in maintaining the coolness of the refrigerated section. Often, a refrigerated section door that is not closed may remain open for a relatively long period of time if business is slow and employees of the store do not see the opened door.
In the case of sliding glass doors for display cases, for example those for refrigeration units, sometimes the doors will be designed to run slanted relative to the surrounding frame. In such situations, more surfaces of the door come into contact with the surrounding frame, or the wheel units produce greater frictional drag because a more uniform or constant frictional contact is necessary to maintain lateral alignment of the door. Where the running gear are grooved wheels, for example, where the grooved wheels maintain lateral alignment, greater frictional drag is created with a slanted door to maintain the slanted door in alignment. Where the running gear provide lateral alignment, the running gear take the load and wear and tear, and therefore must be stronger or more rugged to withstand the increased wear.
Assemblies for automatically closing a sliding door are well-known in the art. However, automatically returnable sliding doors have design characteristics that can be improved. For instance, conventional sliding door return assemblies return the door at a relatively constant acceleration causing the door to slam shut and possibly not close completely because of bounce back. Further, if the door is opened only partially, the return force developed in the return assembly may not be sufficient to return the door to its fully closed position. The sliding door return assemblies further may be so complex that the sliding door is difficult to remove from its frame structure for service, which makes cleaning of the space between the door and the door frame structure more difficult. In commercial refrigerators and refrigerated display cases, this space must be cleaned on a regular basis to provide an efficient and sanitary unit as well as a clean appearance for customers and inspectors.
Typical sliding door and window units run with grooved wheels on round-topped rails. Depending on the construction, such running gear arrangements may operate sufficiently well for a given operation but may be inefficient in many other applications. For example, the doors may run rough or inefficiently using a grooved wheel-rail arrangement because the grooved wheel has surfaces which continually frictionally engage the rail. As the wheel rotates, the sides of the grooved wheel rub along the rail surface, producing drag. The wheel inherently serves a dual function, by supporting the weight of the door on top of the track and by maintaining transverse or lateral alignment as the sides of the grooved wheel engage the sides of the rail. These areas of contact produce frictional drag throughout the movement of the door.
The amount of frictional drag depends on the particular configuration of the running gear and the door. For example, in a grooved wheel and track configuration, a pair of grooved wheels placed longitudinally close together to run on the same track work against each other where there are curves, bends or other defects in the track. As one wheel follows a bend, the other adjacent wheel tries to remain aligned with the straight portion of the track. As a result, the side of the one wheel engaging the track urges the door in the direction of the bend, while the side of the other wheel contacting the track tries to keep the door aligned with the rest of the track. These counter forces not only create drag but cause the door to move unevenly and result in premature and undue wear in the running gear or track.
Frictional drag adversely affects not only smooth movement of the door, but also the operation of any self-return mechanism or other apparatus which relies on smooth operation of the door. With greater frictional drag in the running gear, for example, the self-return mechanism must be made stronger for proper functioning to overcome the increased frictional drag caused by the running gear. A stronger self-return mechanism necessarily shifts the range of operation of the self-return mechanism. A strong self-return mechanism means that the door might not be used in situations where only a more efficient or smooth running door would be used because a strong return may cause damage or limit the uses for the door. For example, a stronger self-return mechanism may cause a door to slam shut, and may preclude complete closing of a sliding glass door, for example, and also may cause injury to the user because of more force being created during the closing.
The quality of the running gear also affects the lifetime of the door or other structure as a whole. For example in door applications, many running gear units are rivetted or otherwise non-removably fastened to the bottom of the door. Therefore, if the running gear fails, the entire door must be replaced. Consequently, the life time and durability of the running gear typically determines the useful life of the entire door structure.
In order to incorporate a running gear into a sliding display door, for example, where the viewing area is important, the clearance of the door for installation and the appearance of the door after it is installed is important. For example, as the door is lifted into the frame to be installed, there must be sufficient clearance for the bottom of the door to get over the bottom of the frame and fall down into the frame. Thereafter, the door should appear symmetric in its surrounding frame so that the glass area in the door is centered in the frame for example and so that any trim is uniform around the surrounding frame. The wheel or other supporting structure under the door should not be so large that the door sits too high in the surrounding frame, but larger wheel units are preferable for smooth running and adequate support of the weight of the door. Additionally, the surrounding frame should not be too small on the bottom, for allowing the door to be placed into the frame, because the lower frame line would then expose more of the door structure, and maybe even show some of the running gear.
One aspect of running gear that is important to structures such as sliding glass doors is the size of the running gear. As the size is significant to sliding glass doors, this discussion with respect to the size of the running gear will be made in the context of sliding glass doors. Typically, the size of the surrounding frame is determined by the size of the opening such as for a refrigeration unit, case or opening which is filled by the sliding glass doors. Furthermore, the aesthetic appearance of the doors is quite often important, and it is often difficult to ensure symmetry of the door appearance around all four sides of the surrounding frame. For example, the top of the surrounding frame often extends downwardly more than the bottom of the surrounding frame extends upwardly, so that door installation is made easier when inserting the top of the door into the top of the frame and then pushing the bottom of the door over the bottom surrounding frame with sufficient clearance. The sliding glass door is then dropped into the bottom of the frame while the top of the door is still guided by and retained in the top frame. If the running gear is vertically too large, the top of the frame often must be higher, if the opening allows, so that the top of the door can extend farther into the top of the frame before the door clears the bottom of the frame; or the bottom of the frame must be made smaller so as to allow the door to clear the frame. As a result, sometimes the running gear on the bottom of the door shows above the bottom of the surrounding frame, or more of the bottom rail of the door is visible than the top rail of the door. Therefore, the design of the running gear including its size is quite significant.
Another aspect of the size of the running gear is significant in sliding glass doors, for example. In situations where the sliding glass doors are intended to operate on a slant, such as for some refrigeration units, oversized running gear shifts the doors upward relative to the surrounding frame. If the doors ride too high with the running gear relative to the surround frame, the bottom door rail may not contact the frame wall. Contact by the bottom door rail with the surrounding bottom frame is often necessary or desirable in order to provide support for the bottom of the door as the door moves in the frame. Changes would then be necessary to the surrounding frame to accommodate the sliding doors having oversized or overly large running gear.
The track configuration is also often significant in the operation and integrity of running gear and the structures they support. For example, tracks which are embedded or integral with the frame structure supporting them often suffer from the same defects or design problems inherent in or built into the supporting frame. For example, in the context of sliding glass doors, an embedded track would be as crooked or bumpy as the frame where, for example, the cabinet face in which the frame is set is not flush or straight, where the cabinet face is twisted or the surrounding frame is twisted, bent or where the opening in the cabinet is badly cut or formed. In the context of refrigeration cases, occasionally the so-called net opening is cut poorly. The installed surrounding frame then adopts the shape or form of the net opening, and an embedded track also takes on the defective shape. Other problems may arise such as where the frame is improperly installed.
Accordingly, one principal object of the present invention is to provide a self return mechanism for a closure which controls the return of the closure from a first position to a second position.
A further object of the present invention is to provide a door return which varies the acceleration and deceleration or rate of return of the door as it is automatically closed, to prevent the door from slamming into the door frame and not closing fully, to fully close the door regardless of how far the door has been opened, and to improve the safety of the door.
Another object of the present invention is to provide a self return mechanism where the rate of return of the door is subtly controlled by the use of a closing mechanism which provides a force capable of decreasing the rate of return of the door when it is automatically closed from its opened position without slamming the door into the door frame and which provides a force sufficient to close the door even when it is opened only partially.
A further object of the present invention is to provide a self return mechanism using varying frictional interaction between a portion of an elastic element and a braking element through which the elastic element passes to vary the rate of return of the door. This interaction could occur, for example, between a latex cord or tube elastic element and a grooved wheel whereby stretching and relaxing of the elastic element varies the frictional interaction between the elastic element and the wheel.
Another object of the present invention is to provide a slider door return system which allows for easy removal and replacement of the door from the door frame structure.
It is yet another object of the present invention to provide a slider door return system which is inexpensive to manufacture and simple to assemble.
It is yet a further object of one embodiment of the present invention to provide a slider door return system having the objects stated above for slanted sliding doors.
It is another object of the present invention to provide a wheel unit which minimizes the frictional engagement between the wheel and a track on which the wheel rides.
It is a further object of the present invention to provide a wheel and track unit which minimizes the surface contact between the wheel and a supporting rail to maintain the wheel on the track.
It is a further object of the present invention to provide a running gear unit for doors, closures and other moving structures which can be easily replaced on the structure, if the running gear fails unexpectedly, without having to replace the entire structure.
It is a further object of the present invention to provide a running gear mechanism which has a relatively low vertical profile, and which permits a larger viewing area for a door such as a sliding refrigerator door which is supported by the running gear.
It is another object of the present invention to provide a running gear mechanism which is simpler and easier to manufacture and assemble relative to previous running gear units.
It is a further object of the present invention to provide a wheel unit for supporting and transporting a structure wherein the wheel unit is self-aligning.
It is an additional object of the present invention to provide a wheel and track unit for supporting a structure for movement on the track which uses a track guide separate from the wheel riding on the track.
It is an additional object of the present invention to provide a wheel unit which provides smoother and more reliable operation for the supported structure.
It is a further object of the present invention to provide a wheel unit which can be easily cleaned to ensure sanitary conditions, such as those which may be required by statute or regulation.
It is a still further object of the present invention to provide a free floating track for supporting the wheel units and supported structures which may be self-aligning and which may be free to move as the structure travels over the track.
It is a further object of the present invention to provide a free floating track which is not subject to the design characteristics of the frame which supports the track.
These and other objects are provided in accordance with the present invention described herein.